Discrimination between recent (primary) and past cytomegalovirus (CMV)
infection can be an important tool in the clinical management of
transplant recipients and pregnant women. Although nearly all
individuals with recent CMV infection are positive for CMV IgM,
individuals with past CMV may also express CMV IgM following viral
reactivation; thus, detection of CMV IgM is not a reliable indicator of
recent infection. Measurement of CMV IgG avidity can assist in
discriminating recent from past CMV infection. Although a low avidity
index is a reliable indicator of CMV infection within the previous 6
months, a high avidity index is more meaningful from a clinical
standpoint; a high avidity index essentially excludes the possibility
that infection occurred within the previous 4 months.
In summary, assessment of CMV-specific IgG avidity is an extremely
powerful tool for estimating the time of CMV infection. Such
information is particularly important in the clinical management of
pregnant women found to be positive for CMV antibodies at their first
prenatal visit. Determining the time of primary infection can help
guide decisions regarding antiviral therapy by identifying those women
who should or should not be treated during pregnancy. CMV IgG avidity
measurement also has broad applicability to the management of other
patient groups with an increased risk of debilitating CMV disease, such
as solid organ transplant recipients. Approximately 50% of pregnant
women with primary CMV infection transmit CMV to their infants.
Measuring CMV IgG avidity can reliably distinguish primary infection
from active latent infection during pregnancy.